The endothelial cell under normal physiological conditions serves as non- thrombogenic surface lining all blood vessels. However, upon perturbation by numerous factors such as endotoxin, tumor necrosis factor and antigen- antibody-complement complexes, the endothelial cell surface becomes procoagulant and thrombogenic. Our proposal is to investigate the effect thrombomoduli and protein S of the protein C system (a major antithrombotic mechanism).